The invention relates to a starter device for aft internal combustion engine.
Automotive vehicles, such as tracks, are often equipped with a starter device which drives the internal combustion engine of the vehicle during a starting phase. The starter device includes a pinion which selectively engages a gear connected to the internal combustion engine, e.g. a ring mounted on the flywheel of the engine. The starter device is used only during some sequences and the starting rotation speed may be inferior to the nominal engine rotation speed. To protect the starter motor, which is generally electrically driven, from damages provoked by overspeed and wear, the pinion is engaged with the ring gear only during the starting phase. The starter device therefore comprises an actuation system which engages or disengages the pinion with the ring gear. The actuation system also needs to operate the electrical connection of the starter motor to a power supply of the vehicle.
Known actuation systems comprise an electrical solenoid which moves a plunger linked to a mechanical coupler and an electrical contactor. When electrical current is provided to the solenoid, the subsequent movement of the plunger causes the mechanical coupler to engage the pinion with the ring gear. The electrical contactor then closes an electrical circuit which feeds the starter motor, so that it delivers torque to the internal combustion engine.
The use of such a solenoid implies major drawbacks. This solenoid is made of a significant amount of copper, which is a costly material. As it must generate a relatively long displacement, the volume of the solenoid is significant. The solenoid is therefore relatively heavy and difficult to package within the internal combustion engine arrangement.
To solve this issue, it is known, for example from FR-A-2 886 688, to engage the pinion with the ring gear by using the rotation of the starter motor to cause, the translation of the pinion. A member is engaged to a helical groove of a shaft driven by the starter motor, achieving a helical linkage which drives in translational motion a part which pushes the pinion toward the tins sear.
Such a technique involves a relatively high number of parts including an intermediate part which axially pushes the pinion. Moreover, this intermediate part is also involved in the helical linkage and roust therefore be blocked in rotation, involving additional blocking means and means to permit relative rotation between the pinion and the intermediate part. The starter is therefore complex to assemble.
It is desirable to provide a new starter device in which the helical linkage which produces the translation of the pinion involves fewer parts and works in a less complex way than in the prior art.
An aspect of the invention concerns a starter device for an internal combustion engine, said starter device comprising a starter housing, an electric motor and an engagement pinion driven in rotation by said motor around the pinion rotation axis, the pinion being movable in a translational motion along its pinion rotation axis between a retracted position and an engaging position for engaging a gear connected to the internal combustion engine, the translational motion being caused by the rotation of the electric motor, the starter device further comprising a non-rotatable element which is blocked in rotation with respect to the starter housing, a rotatable element driven in rotation by the electric motor, and a helical linkage between the non-rotatable element and the rotatable element for causing the translational motion of the pinion. This starter device is characterized in that the non-rotatable element is fixed in translation along the pinion rotation axis with respect to the starter housing in that the rotatable element can translate with respect to the starter housing, and in that translation of the rotatable element causes translation of the pinion towards its engaging position.
Thanks to an aspect of the invention, the non-rotatable element of the helical linkage is fixed in translation, instead of being movable in translation to engage the pinion with the flywheel ring. The translation is therefore directly transmitted to the rotatable element, avoiding the use of means to allow relative rotation between the pinion and the rotatable element.
According to further aspects of the invention which are advantageous but not compulsory, such a starter device may incorporate one or several of the following features:                The helical linkage can be deactivated. This permits to more easily return the pinion to its non-engaging position, without needing to reverse the rotation direction of the starter motor.        The non-rotatable element may comprise a retractable clutching member mounted in the starter housing. The retractable clutching member may be movable between a first deactivated position and an activated position with respect to the starter housing. A helical groove may be provided on an outer surface of the rotatable. The retractable clutching member may be engaged in the helical groove when the retractable clutching member is in its activated position.        The rotatable element may comprise a transmission shaft driven by the electric motor and movable in translational movement with respect to the housing, between a first position, in which the pinion is in its non-engaging position, and a second position, in which the pinion can be in its engaging position.        The starter device may comprise a resilient element adapted to urge the transmission shaft towards its first position. This permits to pull back the pinion towards its non-engaging position automatically, without using positive power from the motor for example.        The helical linkage may be deactivated by retracting the retractable clutching member from the helical groove.        An end of the helical groove may open in a peripheral groove, radial to a rotation axis of the rotatable member, in which the retractable clutching member may be received when the pinion is completely engaged with the ring gear. This permits to allow rotation of the pinion without inducing translation of the pinion, without necessarily deactivating the clutching member.        The retractable clutching member can be movable between its first deactivated position and its activated position along a translational movement along a transversal axis.        The retractable clutching member may be movable from its first deactivated position, to a second position where its clutching portion is hi contact with the outer surface of the rotatable element, to a third position where its clutching portion is received in the helical groove and to a fourth position where its clutching portion is received in the peripheral groove. One advantage of this feature is that, by detecting the position retractable clutching member, it can possible to determine in which state the starter is.        
The starter device may comprise a resilient element which urges the retractable clutching member towards its deactivated position.                The feeding of the starter motor with electrical current may be controlled by the movement of the retractable clutching member.        The retractable clutching member may comprise a main contact plate adapted to close a high power circuit for the starter motor (M), for example by making a contact with a first and a second connecting tabs in order to allow nominal power in the starter motor, when the retractable clutching member is in the groove radial to the rotation axis of the pinion, so as to drive the starter motor at a nominal torque or rotation speed. In other words, the main contact plate closes a high power circuit for the starter motor.        The retractable clutching member may comprise a preliminary contact plate adapted to close a low power circuit, for example by making a contact with a third and a fourth connecting tabs in order to allow reduced power in the starter motor, when the retractable clutching member is in the helical groove, so as to drive the starter motor at a low torque or rotation speed. In other words, the preliminary contact plate closes a low power circuit for the starter motor. The depth of the helical groove may be inferior to the depth of the peripheral groove. This permits to engage the pinion with minimal potential damages.        
In the deactivated position of the retractable clutching member, the main and preliminary contact plates and the connecting tabs may be located so that, during the movement of the retractable clutching member towards the helical groove, the contact between the preliminary contact plate and the third and fourth connecting tabs is made before the contact between the main contact plate and the first and second connecting tabs. Thereby, the preliminary contact plate closes the low power circuit before the main contact plate closes the high power circuit.
The preliminary contact plate may close the low power circuit, for example by connecting the third and fourth connecting tabs, when the retractable clutching member is in its second and third positions and the main contact plate may close the high power circuit, for example by connecting the first and second connecting tabs, when the retractable clutching member is in its fourth position.
The main and preliminary contact plates may be movable in translation with respect to the retractable clutching member along a longitudinal axis of the retractable clutching member.
The electrical contact between the preliminary contact plate and the third and fourth connecting tabs may be kept, thereby keeping the low power circuit closed, by a resilient element mounted between the main contact plate and the preliminary contact plate, and the electrical contact between the main contact plate and the first and second connecting tabs may be kept, thereby keeping the high power circuit closed, by a resilient element mounted between the first contact plate and a collar of the retractable clutching member.
The pinion may be movable hi translational movement with respect to the rotatable element, and wherein a resilient element urges the pinion towards an end of the rotatable element located on the side of the ring gear. In case of a tooth-against-tooth situation, this permits to effectively engage the pinion by allowing it to rotate in the right angular position.